All-solid-state cell

ABSTRACT

An all-solid-state cell has a fired solid electrolyte body, a first electrode layer integrally formed on one surface of the fired solid electrolyte body by mixing and firing an electrode active material and a solid electrolyte, and a second electrode layer integrally formed on the other surface of the fired solid electrolyte body by mixing and firing an electrode active material and a solid electrolyte. The first and the second electrode layers are formed by mixing and firing the electrode active material and the amorphous solid electrolyte, which satisfy the relation Ty&gt;Tz (wherein Ty is a temperature at which the capacity of the electrode active material is lowered by reaction between the electrode active material and the solid electrolyte material, and Tz is a temperature at which the solid electrolyte material is shrunk by firing).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2007-293682 filed on Nov. 12, 2007 andJapanese Patent Application No. 2008-268333 filed on Oct. 17, 2008 inthe Japanese Patent Office, of which the contents are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an all-solid-state cell utilizing acombination of an electrode active material and a solid electrolytematerial.

2. Description of the Related Art

In recent years, with the advancement of portable devices such aspersonal computers and mobile phones, there has been rapidly increasingdemand for batteries usable as a power source thereof. In cells of thebatteries for the purposes, a liquid electrolyte (an electrolyticsolution) containing a combustible organic diluent solvent has been usedas an ion transfer medium. The cell using such an electrolytic solutioncan cause problems of solution leakage, ignition, explosion, etc.

In view of solving the problems, all-solid-state cells, which use asolid electrolyte instead of the liquid electrolyte and contain onlysolid components to ensure intrinsic safety, have been developing. Theall-solid-state cell contains a sintered ceramic as the solidelectrolyte, and thereby does not cause the problems of ignition andliquid leakage, and is hardly deteriorated in battery performance bycorrosion. Particularly all-solid-state lithium secondary cells canachieve a high energy density easily, and thus have been activelystudied in various fields (see, for example, Japanese Laid-Open PatentPublication Nos. 2000-311710 and 2005-063958, Yusuke Fukushima and fourothers, “Fabrication of electrode-electrolyte interface inall-solid-state cell lithium batteries using the thermal softeningadhesion behavior of Li ₂ S—P ₂ S ₅ glass electrolytes”, Lecture Summaryof Chemical Battery Material Association Meeting, Vol. 9th, Pages 51-52,issued on Jun. 11, 2007)

Japanese Laid-Open Patent Publication No. 2005-063958 discloses athin-film, solid, lithium ion secondary cell. The secondary celldescribed in Japanese Laid-Open Patent Publication No. 2005-063958 is abendable thin-film cell having a flexible solid electrolyte and thinlayers of positive and negative electrode active materials sputteredthereon. The electrodes of the cell have to be thin, and the amounts ofthe electrode active materials are limited. Thus, the cell isdisadvantageous in that it is difficult to achieve a high capacity.

The article of Fukushima et al. reports formation of anelectrode-electrolyte interface of a complex of a glass electrolyte andan electrode active material, utilizing softening fusion of the glasselectrolyte. In this report, it is described that the resistance betweenelectrolyte particles is effectively lowered due to the fusion of theglass electrolyte, and further a heterophase is not formed in a reactionbetween the electrolyte and the active material.

However, an all-solid-state cell having positive and negative electrodesis not described in this report, and it is unclear whether the reactionresistance can be lowered in the electrolyte-electrode active materialinterface. Further the relation between the electric properties and thefact that the heterophase is not formed is not specifically described,and the charge-discharge ability of the all-solid-state cell is unknown.Furthermore, the electrolyte used in this report is a sulfide, which isexpected to be unstable in the atmosphere (air). The electrolyte maygenerate a toxic gas when brought into contact with the air due tobreakage or the like. Thus, this technology is disadvantageous insafety.

The internal resistance of a cell is partly due to an interface betweenan electrode active material and an electrolyte. The resistance againsttransfer of electrons and Li ions through the interface during chargeand discharge is hereinafter referred to as the interface reactionresistance. The present invention relates to a technology for loweringthe interface reaction resistance in an all-solid-state cell systemusing a solid electrolyte.

For example, in the conventional lithium ion cell using the electrolyticsolution, the electrolyte is a liquid containing an organic solvent,though the electrode active material is a solid. Therefore, theelectrolyte can readily penetrate between particles of the electrodeactive material to form an electrolyte network in the electrode layers,resulting in a low interface reaction resistance.

In terms of the interface reaction resistance according to the presentinvention, a reaction resistance per unit area of connected particleslargely depends on the combination of the active material and theelectrolyte to be used. As the connected area between the particles isincreased, the interface reaction resistance of the entire cell islowered and the internal resistance is lowered such that resistances areparallel-connected in an equivalent circuit. Thus, the interfacereaction resistance between the electrolyte and the active material canbe lowered by (1) selecting the material combination in view of smoothlytransferring the Li ions and (2) increasing the connection interfacearea between the electrolyte and the active material per an electrodecapacity.

In the present invention, a combination of an electrode active materialand a solid electrolyte containing a common polyanion or a combinationof an electrode active material and a solid electrolyte of phosphatecompounds is used in view of the process of (1), and a solid electrolyteis mixed with an electrode active material to form a network in anelectrode layer, whereby the connection interface area between theelectrode active material and the solid electrolyte is remarkablyincreased to lower the interface reaction resistance in view of theprocess of (2).

Japanese Laid-Open Patent Publication No. 2000-311710 discloses a solidelectrolyte cell containing a solid electrolyte material of an inorganicoxide, which forms a three-dimensional network between particles of anelectrode active material. Thus, the inventors have selected thecombination of the phosphate compounds containing a common polyanion asthe combination of the electrode active material and the solidelectrolyte suitable for smoothly transferring the Li ions, and haveproduced an all-solid-state cell having electrodes containing the solidelectrolyte between the electrode active material particles. However,because the solid electrolyte was fired in the state of a mixture withthe electrode active material in the electrode layer, the electrolytewas reacted with the active material, so that reduction in the peakintensity of the active material and formation of a heterophase werefound in an XRD (X-ray diffraction) observation. The active material inthis state was subjected to a charge-discharge ability measurement usingan ideal system containing an electrolytic solution. As a result, thecharge-discharge capacity of the active material was extremely reduced,and the active material was incapable of charge and discharge at itsoriginal theoretical capacity. Thus, the capacity of the electrodeactive material was lowered.

Then, the inventors have lowered the firing temperature to prevent thereaction between the electrode active material and the solidelectrolyte. However, the solid electrolyte particles were notsufficiently sintered, the particle boundary resistance between thesolid electrolyte particles was increased, and the connection interfacearea between the electrode active material and the solid electrolyte wasnot increased. As a result, both the particle boundary resistance of thesolid electrolyte and the interface reaction resistance of the electrodeactive material and the solid electrolyte could not be lowered, wherebythe resultant all-solid-state cell had no charge-discharge capacity (nocharge-discharge ability).

SUMMARY OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide such an all-solid-state cell that the particle boundaryresistance of a solid electrolyte can be lowered in an electrode layerwhile preventing capacity reduction due to a reaction of the solidelectrolyte with an electrode active material, a network of the solidelectrolyte can be formed in the electrode layer, the connectioninterface area between the solid electrolyte and the electrode activematerial can be remarkably increased to lower the interface reactionresistance, and thus charge and discharge can be carried out even in theall solid state.

In research of an all-solid-state cell having an electrode layercomposed of a mixture of a solid electrolyte material and an electrodeactive material, the inventors have found that the charge-dischargecapacity of the electrode active material is reduced below its originaltheoretical capacity due to reduction in the crystallinity of theelectrode active material and formation of a heterophase by a reactionbetween the solid electrolyte material and the electrode activematerial. Based on this finding, the inventors have further found thatwhen a combination of the materials satisfies the inequality Ty>Tz (inwhich Ty is a temperature at which the capacity of the electrode activematerial is lowered by the reaction, and Tz is an initiation temperatureat which the solid electrolyte material is shrunk by firing), anelectrolyte network can be formed in the electrode layer to lower theresistance within the temperature range of Tz to Ty, the connection areabetween the materials can be increased while preventing the reactionbetween the electrolyte material and the electrode active material, andthe interface reaction resistance at the connection interface betweenthe materials can be lowered, whereby the resultant all-solid-state cellhas a low internal resistance.

In the present invention, a combination of phosphate compoundscontaining a common polyanion may be selected as the combination of anelectrode active material and a solid electrolyte material suitable forsmoothly transferring Li ions, and the solid electrolyte materialcomprising the phosphate compound may be vitrified. In a specificexample, a Nasicon type LAGP having a relatively higher ion conductivityamong the phosphate compounds was vitrified, and the resultant solidelectrolyte material had low transition temperatures, Tg (glasstransition point) of approximately 480° C. and Tx (crystallizationtemperature) of approximately 590° C. (see FIG. 10). This glass materialhad a firing shrinkage initiation temperature of 550° C. to 600° C.Then, the reactivity between this vitrified solid electrolyte materialand the electrode active material was evaluated, and crystallinityreduction and heterophase formation were not observed even at atemperature sufficiently higher than the firing shrinkage initiationtemperature. Thus, the novel combination of the phosphate compoundmaterials containing a common polyanion satisfied the relation of Ty>Tz.

As a result, the inventors found a condition for preventing thedeterioration in the charge-discharge ability of the electrode activematerial due to the reaction between the electrode active material andthe solid electrolyte material while maintaining sufficient connectionof the solid electrolyte particles. The above problems were solved basedon this finding.

By using such materials for forming the mixture electrode layer of theall-solid-state cell, the particle boundary resistance between the solidelectrolyte particles could be lowered while preventing the reduction inthe capacity of the electrode active material, and the electrolytenetwork could be formed in the electrode layer. Therefore, theconnection interface area between the electrode active material and thesolid electrolyte material could be remarkably increased to lower theinterface reaction resistance, and thus the resultant all-solid-statecell was capable of charge and discharge operations even in the allsolid state.

Thus, an all-solid-state cell according to the present inventioncomprises positive and negative electrode portions containing anelectrode active material, an electrolyte portion containing a solidelectrolyte, and positive and negative collector portions, and ischaracterized in that the one or both of the positive and negativeelectrode portions are formed by mixing and firing the electrode activematerial and an amorphous solid electrolyte material, which satisfy theinequality:

Ty>Tz

wherein Ty is a temperature at which the capacity of the electrodeactive material is lowered by a reaction between the electrode activematerial and the solid electrolyte material, and Tz is a temperature atwhich the solid electrolyte material is shrunk by firing.

Specifically, Tz is a temperature at which the relative density of thesolid electrolyte material is increased to 70% or more of thetheoretical density thereof due to the firing shrinkage. Tz ispreferably a temperature at which the relative density of the materialis increased to 80% or more due to the firing shrinkage within thetemperature range of Ty>Tz.

Specifically, Ty is a temperature at which the charge-discharge capacityof the electrode active material is lowered below 50% of the originaltheoretical capacity thereof. Ty is preferably a temperature at whichthe charge-discharge capacity of the electrode active material is 80% ormore of the theoretical capacity within the temperature range of Ty>Tz.

In the present invention, the solid electrolyte material may comprise anamorphous polyanion compound, and the one or both of the positive andnegative electrode portions may be formed by mixing and firing theelectrode active material and the solid electrolyte material.Alternatively, the solid electrolyte material may comprise an amorphousphosphate compound, and the one or both of the positive and negativeelectrode portions may be formed by mixing and firing the electrodeactive material and the solid electrolyte material.

In the present invention, the solid electrolyte material comprising thephosphate compound may be of Nasicon type after the firing. In thiscase, the phosphate compound of the solid electrolyte material may beLAGP Li_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ or LATP Li_(1+x)Al_(x)Ti_(2−x)(PO₄)₃(0≦x≦1).

In the present invention, the electrode active material may be a Nasicontype material comprising a phosphate compound. In this case, thephosphate compound of the electrode active material may be LVPLi_(m)V₂(PO₄)₃ (1≦m≦5).

In the present invention, the electrode active material for the positiveelectrode portion may be an olivine type positive electrode activematerial comprising a phosphate compound. In this case, the phosphatecompound of the positive electrode active material may be LNPLi_(n)NiPO₄, LCP Li_(n)CoPO₄, LMP Li_(n)MnPO₄ or LFP Li_(n)FePO₄(0≦n≦1).

In the present invention, the solid electrolyte material and theelectrode active material may be of Nasicon type after the firing.

In the present invention, the all-solid-state cell may have such asymmetrical structure that the solid electrolyte material and theelectrode active material are of Nasicon type, the solid electrolytematerial comprises LAGP Li_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ (0≦x≦1, preferably0.3≦x≦0.7), and the electrode active material comprises LVPLi_(m)V₂(PO₄)₃ (1≦m≦5) in both the positive and negative electrodeportions.

In the present invention, the one or both of the positive and negativeelectrode portions may be formed by firing under an applied pressure. Inthis case, by the firing under an applied pressure, a densemicrostructure can be formed in the one or both of the positive andnegative electrode portion, the interface area between the electrodeactive material and the solid electrolyte material can be increased, andthe interface charge transfer resistance can be lowered.

In the present invention, one or both of the positive and negativeelectrode portions may be formed from a paste for printing by firing itunder an inert atmosphere. In this case, a binder component can becarbonized to ensure the electron conductivity of the electrode portion.Thus, the electron conductivity of the electrode portion can bemaintained without intentional addition of a carbon component useful asan electron conducting aid.

As described above, in the all-solid-state cell of the presentinvention, the particle boundary resistance between the solidelectrolyte particles can be lowered while preventing the reduction inthe capacity of the electrode active material in the electrode layer.

Furthermore, in the present invention, since the electrolyte network canbe formed in the electrode layer, the connection interface area betweenthe electrode active material and the solid electrolyte material can beremarkably increased, the interface reaction resistance can be lowered,and thus the resultant all-solid-state cell is capable of charge anddischarge operations even in the all solid state.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a structure of anall-solid-state cell according to an embodiment of the presentinvention;

FIG. 2 is a schematic cross-sectional view showing a structure of anall-solid-state cell according to a modification example of theembodiment;

FIG. 3A is an SEM photograph at ×1000 magnification showing a crosssection of a crystalline LAGP solid electrolyte sintered at a firingtemperature (600° C.) under an Ar atmosphere;

FIG. 3B is an SEM photograph at ×5000 magnification showing a crosssection of a crystalline LAGP solid electrolyte sintered at a firingtemperature (600° C.) under an Ar atmosphere;

FIG. 4A is an SEM photograph at ×1000 magnification showing a crosssection of the crystalline LAGP solid electrolyte sintered at adifferent firing temperature (700° C.) under the Ar atmosphere;

FIG. 4B is an SEM photograph at ×5000 magnification showing a crosssection of the crystalline LAGP solid electrolyte sintered at adifferent firing temperature (700° C.) under the Ar atmosphere;

FIG. 5A is an SEM photograph at ×1000 magnification showing a crosssection of the crystalline LAGP solid electrolyte sintered at adifferent firing temperature (800° C.) under the Ar atmosphere;

FIG. 5B is an SEM photograph at ×5000 magnification showing a crosssection of the crystalline LAGP solid electrolyte sintered at adifferent firing temperature (800° C.) under the Ar atmosphere;

FIG. 6A is an SEM photograph at ×1000 magnification showing a crosssection of a vitrified LAGP solid electrolyte sintered at a firingtemperature (550° C.) under an Ar atmosphere;

FIG. 6B is an SEM photograph at ×5000 magnification showing a crosssection of a vitrified LAGP solid electrolyte sintered at a firingtemperature (550° C.) under an Ar atmosphere;

FIG. 7A is an SEM photograph at ×1000 magnification showing a crosssection of the vitrified LAGP solid electrolyte sintered at a differentfiring temperature (600° C.) under the Ar atmosphere;

FIG. 7B is an SEM photograph at ×5000 magnification showing a crosssection of the vitrified LAGP solid electrolyte sintered at a differentfiring temperature (600° C.) under the Ar atmosphere;

FIG. 8A is an SEM photograph at ×1000 magnification showing a crosssection of the vitrified LAGP solid electrolyte sintered at a differentfiring temperature (650° C.) under the Ar atmosphere;

FIG. 8B is an SEM photograph at ×5000 magnification showing a crosssection of the vitrified LAGP solid electrolyte sintered at a differentfiring temperature (650° C.) under the Ar atmosphere;

FIG. 9A is an SEM photograph at ×1000 magnification showing a crosssection of the vitrified LAGP solid electrolyte sintered at a differentfiring temperature (700° C.) under the Ar atmosphere;

FIG. 9B is an SEM photograph at ×5000 magnification showing a crosssection of the vitrified LAGP solid electrolyte sintered at a differentfiring temperature (700° C.) under the Ar atmosphere;

FIG. 10 is a graph showing a DTA (differential thermal analysis)property of the vitrified LAGP solid electrolyte;

FIG. 11 is a characteristic diagram showing changes of the firingshrinkage and the internal impedance of the crystalline LAGP solidelectrolyte depending on the firing temperature;

FIG. 12 is a characteristic diagram showing changes of the firingshrinkage and the internal impedance of the vitrified LAGP solidelectrolyte depending on the firing temperature;

FIG. 13 is a diagram showing the XRD (X-ray diffraction) characteristicsof a fired mixture pellet of an LAGP crystal powder and an LVP crystalpowder;

FIG. 14 is a characteristic diagram showing a peak intensity (peakheight) relation between a main peak of the positive electrode activematerial (the fired mixture pellet of the LAGP crystal powder and theLVP crystal powder) and a main peak of LiVP₂O₇ identified as aheterophase peak, and the change in the discharge capacity of thepositive electrode active material;

FIG. 15 is a diagram showing the XRD (X-ray diffraction) characteristicsof a fired mixture pellet of an LAGP glass powder and an LVP crystalpowder;

FIG. 16 is a characteristic diagram showing a peak intensity (peakheight) relation between a main peak of the positive electrode activematerial (the fired mixture pellet of the LAGP glass powder and the LVPcrystal powder) and a main peak of LiVP₂O₇ identified as a heterophasepeak, and a change in the discharge capacity of the positive electrodeactive material;

FIG. 17 is a graph showing the charge/discharge property of Example 1using the LAGP glass powder;

FIG. 18 is a graph showing the alternating-current impedance property ofExample 1;

FIG. 19 is a graph showing the charge/discharge property of Example 2using the LAGP glass powder;

FIG. 20 is a graph showing the alternating-current impedance property ofExample 2;

FIG. 21 is a graph showing the charge/discharge property of ComparativeExample 1 using the LAGP crystal powder;

FIG. 22 is a graph showing the alternating-current impedance property ofComparative Example 1;

FIG. 23 is a graph showing the charge/discharge property of ComparativeExample 2 using the LAGP crystal powder;

FIG. 24 is a graph showing the alternating-current impedance property ofComparative Example 2;

FIG. 25 is a graph showing the charge/discharge property of Example 3;and

FIG. 26 is a graph showing the alternating-current impedance property ofExample 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the all-solid-state cell of the present invention willbe described below with reference to FIGS. 1 to 26.

As shown in FIG. 1, an all-solid-state cell 10 according to thisembodiment comprises a combination of an electrode active material and asolid electrolyte material. The all-solid-state cell 10 has a firedsolid electrolyte plate 14 of a ceramic containing a solid electrolyte12, a first electrode layer 18 (e.g. a positive electrode) integrallyformed on one surface of the fired solid electrolyte plate 14 by mixingand firing an electrode active material 16 and a solid electrolyte 12, asecond electrode layer 20 (e.g. a negative electrode) integrally formedon the other surface of the fired solid electrolyte plate 14 by mixingand firing an electrode active material 16 and a solid electrolyte 12, afirst collector electrode 24 electrically connected to the firstelectrode layer 18, and a second collector electrode 26 electricallyconnected to the second electrode layer 20.

In the all-solid-state cell 10, the fired solid electrolyte plate 14substantially acts as a solid electrolyte portion separating thepositive and negative electrodes. The solid electrolyte 12 contained inthe ceramic of the fired solid electrolyte plate 14 is not particularlylimited, and may be selected from known conventional solid electrolytes.The solid electrolyte 12 preferably contains a lithium ion as a movableion, and examples thereof include lithium ion-conductive solid glasselectrolytes such as Li₃PO₄, LiPON (Li₃PO₄ mixed with nitrogen),Li₂S—SiS₂, Li₂S—P₂S₅, and Li₂S—B₂S₃, and lithium ion-conductive solidelectrolytes prepared by doping the glass with a lithium halide (e.g.LiI) or a lithium oxoate (e.g. Li₃PO₄). The solid electrolyte 12 isparticularly preferably a titanium oxide type solid electrolytecontaining lithium, titanium, and oxygen, such as Li_(x)La_(y)TiO₃(0≦x≦1, 0≦y≦1), or a Nasicon type phosphate compound such asLi_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ or Li_(1+x)Al_(x)Ti_(2−x)(PO₄)₃ (0≦x≦1),which can exhibit a stable performance even in the case of firing underan oxygen atmosphere.

The thickness of the fired solid electrolyte plate 14 is notparticularly limited, and is preferably 5 μm to 1 mm, more preferably 5μm to 100 μm.

In the first electrode layer 18 and the second electrode layer 20, alarge number of powder particles of the solid electrolyte 12 are bondedby sintering to form a porous body. In the porous body, a plurality ofpores are three-dimensionally connected from the surface to the inside,and are filled with the electrode active material 16. Such a porousbody, formed by bonding the powder particles of the solid electrolyte 12by the sintering, is also referred to as an electrolyte network.

The thicknesses of the first electrode layer 18 and the second electrodelayer 20 are not particularly limited, and are preferably 5 μm to 1 mm,more preferably 5 μm to 500 μm.

In the formation of the first electrode layer 18 and the secondelectrode layer 20, a first paste for forming the first electrode layer18 and a second paste for forming the second electrode layer 20 may beprinted into electrode patterns on the fired solid electrolyte plate 14respectively using a screen printing method, etc.

The first and second pastes may be produced by the steps of dissolving abinder in an organic solvent to prepare a solution, adding anappropriate amount of the solution to powders of the electrode activematerial and the solid electrolyte material to be hereinafter described,and kneading the resultant mixture.

Then, the electrode patterns of the first and second pastes printed onthe fired solid electrolyte plate 14 may be fired at a temperature lowerthan a temperature for forming the fired solid electrolyte plate 14, toform the first electrode layer 18 and the second electrode layer 20. Theobtained first electrode layer 18 and second electrode layer 20 are theporous bodies having a large number of pores filled with the electrodeactive material 16.

Though both the first electrode layer 18 and the second electrode layer20 formed on the fired solid electrolyte plate 14 are composed of aceramic containing a mixture of the electrode active material 16 and thesolid electrolyte 12 in the above example, the second electrode layer 20may be composed of a metal film 22 of a Li metal or Li alloy, like anall-solid-state cell 10 a according to another example shown in FIG. 2.

In this embodiment, the solid electrolyte material added to the firstelectrode layer 18 and the second electrode layer 20 may comprise anamorphous polyanion compound, and the layers may be formed by firing thecompound.

In this embodiment, the solid electrolyte material added to the firstelectrode layer 18 and the second electrode layer 20 may comprise anamorphous phosphate compound, and the layers may be formed by firing thecompound.

The solid electrolyte material comprising the phosphate compound may beof Nasicon type after the firing, and the phosphate compound isparticularly preferably LAGP Li_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ or LATPLi_(1+x)Al_(x)Ti_(2−x)(PO₄)₃ (0≦x≦1).

The electrode active material may be a Nasicon type material comprisinga phosphate compound, and the phosphate compound is particularlypreferably LVP Li_(m)V₂(PO₄)₃ (1≦m≦5).

The positive electrode active material may be an olivine type materialcomprising a phosphate compound, and the phosphate compound isparticularly preferably LNP Li_(n)NiPO₄, LCP Li_(n)CoPO₄, LMPLi_(n)MnPO₄ or LFP Li_(n)FePO₄ (0≦n≦1).

In this embodiment, the solid electrolyte material and the electrodeactive material comprising the phosphate compounds may be of Nasicontype after the firing. In this case, it is preferred that the solidelectrolyte material comprises LAGP Li_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ (0≦x≦1,preferably 0.3≦x≦0.7), and both the positive and negative electrodeactive materials comprise LVP Li_(m)V₂(PO₄)₃ (1≦m≦5), whereby theall-solid-state cell has a symmetrical structure.

Thus, in this embodiment, in the first electrode layer 18 and the secondelectrode layer 20 of the all-solid-state cell 10, the particle boundaryresistance between the solid electrolyte particles can be lowered whilepreventing formation of a heterophase due to a reaction between thesolid electrolyte material and the electrode active material 16.

Furthermore, in this embodiment, the electrolyte network can be formedin the first electrode layer 18 and the second electrode layer 20,whereby the connection interface area between the electrode activematerial 16 and the solid electrolyte 12 can be remarkably increased tolower the interface reaction resistance, and thus the resultantall-solid-state cell 10 is capable of charge and discharge operationseven in the all solid state.

The first electrode layer 18 and the second electrode layer 20 arepreferably formed by firing under an applied pressure. In this case, bythe firing under an applied pressure, a dense microstructure can beformed in the electrode portion, the interface area between theelectrode active material and the solid electrolyte material can beincreased, and the interface charge transfer resistance can be lowered.

The methods for firing the layers under an applied pressure include aHot Isostatic Pressing HIP, in which a mixture is heated at a hightemperature while pressure is simultaneously and isotropically appliedto the mixture, and a Hot Pressing, in which a mixture housed in afiring jig is heat-treated as a whole while pressure is uniaxiallyapplied to the mixture. When using the HIP, a gas such as argon can beused as a pressure medium to apply isotropic pressure to the mixture.

The first electrode layer 18 and/or the second electrode layer 20 may beformed from a paste for printing by firing it under an inert atmospheresuch as an Ar atmosphere. In this case, a binder component can becarbonized to ensure the electron conductivity of the first electrodelayer 18 and/or the second electrode layer 20. Thus, the electronconductivity of the first electrode layer 18 and/or the second electrodelayer 20 can be maintained without intentional addition of a carboncomponent useful as an electron conducting aid.

Examples of the all-solid-state cell 10 according to the embodiment willbe described in detail below.

In Examples, the following Nasicon type phosphate compounds were used asa solid electrolyte material and an electrode active material.

-   Solid electrolyte material: LAGP Li_(1.5)Al_(0.5)Ge_(1.5)(PO₄)₃-   Electrode active material: LVP Li₃V₂(PO₄)₃

[Preparation of Crystal Powder]

First, powders of Li₂CO₃, GeO₂, Al₂O₃, and NH₄H₂(PO₄)₃ were mixed at thestoichiometric composition ratio and fired at 900° C. in the air, sothat a crystal powder of the solid electrolyte materialLi_(1.5)Al_(0.5)Ge_(1.5)(PO₄)₃ (LAGP) (hereinafter referred to as theLAGP crystal powder) was prepared by a solid-phase synthesis method.

Meanwhile, powders of Li₂CO₃, V₂O₃, and NH₄H₂(PO₄)₃ were mixed at thestoichiometric composition ratio and fired at 930° C. in an Ar flow, sothat a crystal powder of the positive (negative) electrode activematerial Li₃V₂(PO₄)₃ (LVP) (hereinafter referred to as the LVP crystalpowder) was prepared by a solid-phase synthesis method.

[Production of Fired Solid Electrolyte Body]

The above obtained LAGP crystal powder was press-formed using a moldinto a compact powder pellet having a diameter of 16 mm and a thicknessof approximately 1 mm. The pressure for the forming was 500 kg/cm². Thepellet was fired at 840° C. in the air to obtain a fired solidelectrolyte pellet of LAGP.

[Preparation of Glass Powder (Vitrification of LAGP Solid Electrolyte)]

The LAGP crystal powder obtained by the solid-phase method was put in aPt crucible and placed in a furnace under an air atmosphere heated at1200° C. for 1 hour. Then, the LAGP crystal powder was taken out andrapidly cooled by iced water, to obtain a vitrified LAGP. The vitrifiedLAGP was pulverized using a mortar, a ball mill, etc. to prepare a fineLAGP glass powder.

[Sintering Property Comparison of Solid Electrolytes]

A solid electrolyte pellet of the LAGP crystal powder (hereinafterreferred to as the crystalline LAGP solid electrolyte) and a solidelectrolyte pellet of the LAGP glass powder (hereinafter referred to asthe vitrified LAGP solid electrolyte) were produced, and the sinteredstates of the pellets were compared at different firing temperaturesunder an Ar atmosphere. The results of SEM observation of fracture crosssections in the pellets are shown in FIGS. 3A and 3B to 9A and 9B, andshrinkage properties of the pellets due to the firing under the Aratmosphere are shown in the graphs of FIGS. 11 and 12.

FIGS. 3A and 3B to 5A and 5B include SEM photographs showing crosssections of the crystalline LAGP solid electrolyte fired at 600° C.,700° C., and 800° C. Each of FIGS. 3A, 4A and 5A is an SEM photograph at×1000 magnification, and each of FIGS. 3B, 4B and 5B is an SEMphotograph at ×5000 magnification. FIGS. 6A and 6B to 9A and 9B includeSEM photographs showing cross sections of the vitrified LAGP solidelectrolyte fired at 550° C., 600° C., 650° C., and 700° C. Each ofFIGS. 6A, 7A, 8A and 9A is an SEM photograph at ×1000 magnification, andeach of FIGS. 6B, 7B, 8B and 9B is an SEM photograph at ×5000magnification.

FIG. 10 is a graph showing a DTA (differential thermal analysis)property of the vitrified LAGP solid electrolyte in an inert atmosphere(N₂ atmosphere). It is clear from FIG. 10 that the vitrified LAGP solidelectrolyte had low transition temperatures, Tg (glass transition point)of approximately 480° C. and Tx (crystallization temperature) ofapproximately 590° C.

FIG. 11 is a characteristic diagram showing changes of the firingshrinkage (%) and the internal impedance of the crystalline LAGP solidelectrolyte depending on the firing temperature. FIG. 12 is acharacteristic diagram showing changes of the firing shrinkage (%) andthe internal impedance of the vitrified LAGP solid electrolyte dependingon the firing temperature. In the diagrams, the firing shrinkage of eachLAGP solid electrolyte is shown by plotted black dots, and the internalimpedance is divided into two corresponding to the intraparticleresistance and the particle boundary resistance and shown by bar graph.

As shown in FIGS. 3A and 3B to 5A and 5B, and 11, in the crystallineLAGP solid electrolyte, at a firing temperature of 700° C. or lower, thepowder particles were not sufficiently sintered and maintained theoriginal particle shapes, and the particle boundary resistance wasremarkably high in terms of the internal impedance. On the other hand,as shown in FIGS. 6A and 6B to 9A and 9B, and 12, in the LAGP glasspowder (the vitrified LAGP solid electrolyte), at a firing temperatureof 600° C. or higher, the solid electrolyte material was sufficientlyshrunk by the firing, the particles were suitably bonded to each other,and the particle boundary resistance was significantly lowered in termsof the internal impedance.

[Relation of Reactivity Between Electrolyte and Electrode ActiveMaterial to Charge-Discharge Capacity of Electrode Active Material]

An electron conducting aid of acetylene black was added to a mixture ofthe LAGP crystal powder and the LVP crystal powder to carry out anevaluation using an electrolytic solution later. A powder pellet of themixture was prepared and fired at a firing temperature under an Aratmosphere to obtain a fired body. The obtained fired body was subjectedto an XRD (X-ray diffraction) measurement. The measurement results areshown in FIG. 13. In FIG. 13, peaks of Li₃Fe₂(PO₄)₃ for identifying thecrystal structure of the LVP are marked with black squares, and peaks ofLiGe₂(PO₄)₃ for identifying the crystal structure of the LAGP are markedwith black triangles. The LAGP and the LVP are not registered in ICDD,and thus the compounds having the same crystal structures were used forthe identification. As shown in the measurement results, a plurality ofpeaks of a heterophase derived from a condensed phosphate salt wereobserved in addition to the peaks of the LAGP and LVP at temperatures of700° C. and 800° C., at which the LAGP crystal powder was sintered.

The relations between the charge-discharge capacity of the electrodeactive material, and the peak intensity of the positive electrode activematerial and the peak intensity of the heterophase were evaluated.Specifically, each of the fired mixed powder body pellets, fired at thedifferent temperatures, was pulverized and used in a positive electrodein a liquid type lithium ion cell containing an electrolytic solution(1−mol/L LiClO₄/EC+DEC (volume ratio 1:1) solution) and a negativeelectrode of Li metal, and the charge-discharge ability (capacity) ofthe positive electrode active material was measured. It should be notedthat the LVP has a theoretical charge-discharge capacity of about 130mAh/g. The peak intensity (peak height) relation between the main peak(a) of the positive electrode active material observed in the XRDmeasurement (see FIG. 13) and the main peak (b) of LiVP₂O₇ identified asa heterophase peak, marked with a white circle in FIG. 13, is shown inFIG. 14 as the measurement results. In FIG. 14, the change of thecharge-discharge capacity of the positive electrode active material isshown by plotted black squares. The peak intensities of the main peak(a) of the positive electrode active material and the main peak (b) ofthe heterophase are shown in the bar graph. As shown in the measurementresults, the reduction in the peak intensity of the positive electrodeactive material and the generation of the heterophase derived fromvanadium contained in the positive electrode active materialcorresponded to the reduction in the charge-discharge capacity of thepositive electrode active material. Thus, the capacity reduction due tothe reaction between the solid electrolyte material and the electrodeactive material in the high-temperature firing caused the reduction inthe charge-discharge ability of the electrode active material. It ispossible that the electrode active material was converted to LiVP₂O₇,which was identified beforehand. Further, the electrode active materialexhibited a charge-discharge capacity significantly lower than theoriginal theoretical capacity at temperatures of 700° C. and 800° C., atwhich the LAGP crystal powder was sintered.

An electron conducting aid of acetylene black was added to a mixture ofthe LAGP glass powder and the LVP crystal powder to carry out anevaluation using an electrolytic solution later. A powder pellet of themixture was prepared and fired at a firing temperature under an Aratmosphere to obtain a fired body. The obtained fired body was subjectedto an XRD (X-ray diffraction) measurement. Further, the fired body wasused in a system containing the electrolytic solution, and thecharge-discharge ability of the electrode active material was evaluated.The XRD measurement results are shown in FIG. 15, and thecharge-discharge ability evaluation results are shown in FIG. 16. Theplotted marks in FIGS. 15 and 16 have the same meanings as those inFIGS. 13 and 14.

As shown in FIG. 15, the particles of the LAGP glass powder weresuitably bonded to each other around 600° C. Further, as shown in FIG.16, the electrode active material maintained a sufficient peak intensityand had a charge-discharge capacity close to the original theoreticalcapacity thereof without formation of a heterophase. As a result, thecombination of the materials containing the phosphate compounds using acommon polyanion was considered as a material system satisfying therelation that the temperature, at which the capacity of the electrodeactive material is lowered by the reaction between the electrode activematerial and the solid electrolyte material, is higher than the firingshrinkage initiation temperature of the solid electrolyte material.

[Production of All-Solid-State Cell]

All-solid-state cells having electrodes containing the combinations ofthe electrode active materials and the solid electrolyte materials wereproduced respectively. The electrode was formed by mixing and firing theelectrode active material and the solid electrolyte material of anamorphous LAGP solid electrolyte (an amorphous polyanion (phosphate)compound) in Examples. A crystalline LAGP solid electrolyte was usedinstead of the amorphous LAGP solid electrolyte in Comparative Examples.Examples and Comparative Examples will be described specifically below.

EXAMPLE 1

A binder was dissolved in an organic solvent, and an appropriate amountof the resultant solution was added to the LAGP glass powder and the LVPcrystal powder. The mixture was kneaded in a mortar to prepare anelectrode paste for screen printing. The obtained electrode paste wasprinted into an electrode pattern having a diameter of 12 mm on eachsurface of a fired solid electrolyte body (a base) having a diameter of13 mm and a thickness of 1 mm. The printed electrode patterns were driedto form positive and negative electrodes.

The electrodes were bonded to the surfaces of the solid electrolyte baseby firing at 600° C. for 2 hours using a firing furnace under an Aratmosphere. Then, a sputtered gold (Au) film having a thickness ofapproximately 50 nm was formed as a collector on each surface of theresultant fired body.

After the firing, the positive electrode had a thickness ofapproximately 20 μm and an active material content of approximately 2mg. The charge-discharge capacity per unit weight of the positiveelectrode was calculated from the active material content, and was shownin a graph.

EXAMPLE 2

A binder was dissolved in an organic solvent, and an appropriate amountof the resultant solution was added to the LAGP glass powder and the LVPcrystal powder. The mixture was kneaded in a mortar to prepare anelectrode paste for screen printing. The obtained electrode paste wasprinted into an electrode pattern and dried on each surface of a firedsolid electrolyte body (a base) in the above-mentioned manner, to formpositive and negative electrodes.

The electrodes were bonded to the surfaces of the solid electrolyte baseby firing at 600° C. for 40 hours using a firing furnace under an Aratmosphere. Then, a sputtered Au film was formed on each surface of theresultant fired body.

After the firing, the positive electrode had a thickness ofapproximately 20 μm and an active material content of approximately 2 mgas above.

COMPARATIVE EXAMPLE 1

A binder was dissolved in an organic solvent, and an appropriate amountof the resultant solution was added to the LAGP crystal powder and theLVP crystal powder. The mixture was kneaded in a mortar to prepare anelectrode paste for screen printing. The obtained electrode paste wasprinted into an electrode pattern and dried on each surface of a firedsolid electrolyte body (a base) in the above-mentioned manner, to formpositive and negative electrodes.

The electrodes were bonded to the surfaces of the solid electrolyte baseby firing at 600° C. for 2 hours using a firing furnace under an Aratmosphere. Then, a sputtered Au film was formed on each surface of theresultant fired body.

After the firing, the positive electrode had a thickness ofapproximately 20 μm and an active material content of approximately 2 mgas above.

COMPARATIVE EXAMPLE 2

A binder was dissolved in an organic solvent, and an appropriate amountof the resultant solution was added to the LAGP crystal powder and theLVP crystal powder. The mixture was kneaded in a mortar to prepare anelectrode paste for screen printing. The obtained electrode paste wasprinted into an electrode pattern and dried on each surface of a firedsolid electrolyte body (a base) in the above-mentioned manner, to formpositive and negative electrodes.

The electrodes were bonded to the surfaces of the solid electrolyte baseby firing at 700° C. for 2 hours using a firing furnace under an Aratmosphere. Then, a sputtered Au film was formed on each surface of theresultant fired body.

After the firing, the positive electrode had a thickness ofapproximately 20 μm and an active material content of approximately 2 mgas above.

[Measurement of Alternating-Current Impedance]

The alternating-current impedance of each all-solid-state cell wasmeasured by using 1287 Potentiostat/Galvanostat (trade name) and 1255BFrequency Response Analyzer (trade name) manufactured by Solartron incombination. The measurement frequency was controlled within the rangeof 1 MHz to 0.1 Hz, and the measurement signal voltage was 10 mV.

[Evaluation of Charge-Discharge Property]

Each all-solid-state cell was charged and discharged by a CCCV (ConstantCurrent Constant Voltage) process, and the charge-discharge property wasevaluated. Specifically, in Examples 1 and 2, the all-solid-state cellwas charged at a constant current of 9 μA/cm² to a cutoff voltage of 2.4V and then charged at a constant voltage of 2.4 V to a current value of0.9 μA/cm², and was discharged at a constant current of 9 μA/cm² to acutoff voltage of 0.1 V and then discharged at a constant voltage of 0.1V to a current value of 0.9 μA/cm². In Comparative Examples 1 and 2, theall-solid-state cell was charged at a constant current of 0.9 μA/cm² toa cutoff voltage of 2.4 V and then charged at a constant voltage of 2.4V to a current value of 0.45 μA/cm², and was discharged at a constantcurrent of 0.9 μA/cm² to a cutoff voltage of 0.1 V and then dischargedat a constant voltage of 0.1 V to a current value of 0.45 PA/cm².

(Evaluation)

Each of the produced all-solid-state ceramic cells having the mixtureelectrodes was vacuum-dried under heating and incorporated in a 2032coin cell type package to evaluate the electric properties in a glovebox. The charge-discharge properties of Examples 1 and 2 and ComparativeExamples 1 and 2 are shown in FIGS. 17, 19, 21, and 23. Thealternating-current impedances of Examples 1 and 2 and ComparativeExamples 1 and 2 are shown in FIGS. 18, 20, 22, and 24. In eachalternating-current impedance waveform, the transverse axis indicatesthe real part Z′ of the impedance, the ordinate axis indicates theimaginary part Z″ of the impedance, and the measurement frequencies of 1kHz and 1 Hz are marked with black dots.

(Consideration)

Comparing the charge-discharge capacity, the all-solid-state cells ofComparative Examples 1 and 2 had high internal resistances and werealmost incapable of charge and discharge. In Comparative Example 1, alarge arc corresponding to the particle boundary resistance was formedin a higher frequency region of more than 1 kHz in thealternating-current impedance waveform, and the solid electrolyteparticles were not sufficiently bonded to each other. Thus, the reactioninterface area between the solid electrolyte material and the electrodeactive material was insufficient, whereby the cell of ComparativeExample 1 was almost incapable of charge and discharge. In ComparativeExample 2, a large arc corresponding to the reaction interfaceresistance was formed in a lower frequency region of 1 kHz or less inthe alternating-current impedance waveform. Thus, a heterophase wasformed on the connection interface between the solid electrolytematerial and the electrode active material, and the capacity of theelectrode active material was lowered, whereby the cell of ComparativeExample 2 was almost incapable of charge and discharge.

In contrast, the cell of Example 1 had a low internal resistance and acharge-discharge capacity of approximately 20 mAh/g, and the cell ofExample 2 had a charge-discharge capacity of approximately 40 mAh/g. InExamples 1 and 2, each cell had low impedance in terms of both theparticle boundary resistance and the interface reaction resistance asshown in the alternating-current impedance waveform, since the solidelectrolyte particles were sufficiently bonded in a region of theelectrode layer where a defect (formation of a heterophase, reduction inthe capacity of the active material, etc.) was not generated between thesolid electrolyte material and the electrode active material. The solidelectrolyte material and the electrode active material had an increaseddesirable connection interface, whereby the interface reactionresistance was lowered. Thus, the internal resistance was lowered, sothat the resultant cell was capable of charge and discharge.

EXAMPLE 3

An all-solid-state cell of Example 3 was produced, and thecharge/discharge property and the alternating-current impedance propertywere measured.

In the same manner as Example 1, a binder was dissolved in an organicsolvent, and an appropriate amount of the resultant solution was addedto the LAGP glass powder and the LVP crystal powder. The mixture waskneaded in a mortar to prepare an electrode paste for screen printing.The obtained electrode paste was printed into an electrode patternhaving a diameter of 12 mm on each surface of a fired solid electrolytebody (a base) having a diameter of 13 mm and a thickness of 1 mm. Theprinted electrode patterns were dried to form positive and negativeelectrodes.

The electrodes were bonded to the surfaces of the solid electrolyte baseby firing while applying a load of 500 kg/cm² in the thickness directionat 600° C. for 40 hours using a hot-press furnace under an Aratmosphere. Then, a sputtered gold (Au) film having a thickness ofapproximately 50 nm was formed as a collector on each surface of theresultant fired body.

After the firing, the positive electrode had a thickness ofapproximately 20 μm and an active material content of approximately 2 mgas Example 1.

[Measurement of Alternating-Current Impedance]

The alternating-current impedance of the all-solid-state cell wasmeasured by using 1287 Potentiostat/Galvanostat (trade name) and 1255BFrequency Response Analyzer (trade name) manufactured by Solartron incombination in the same manner as Example 1. The measurement frequencywas controlled within the range of 1 MHz to 0.1 Hz, and the measurementsignal voltage was 10 mV.

[Evaluation of Charge-Discharge Property]

The produced all-solid-state cell was charged and discharged by a CCCVprocess, and the charge-discharge property was evaluated. Specifically,in Examples 3, the all-solid-state cell was charged at a constantcurrent of 90 μA/cm² to a cutoff voltage of 2.4 V and then charged at aconstant voltage of 2.4 V to a current value of 0.9 μA/cm², and wasdischarged at a constant current of 90 μA/cm² to a cutoff voltage of 0.1V and then discharged at a constant voltage of 0.1 V to a current valueof 0.9 μA/cm².

(Evaluation)

The produced all-solid-state ceramic cell having the mixture electrodeswas vacuum-dried under heating and incorporated in a 2032 coin cell typepackage to evaluate the electric properties in a glove box. Thecharge-discharge property of Example 3 is shown in FIG. 25, and thealternating-current impedance of Example 3 is shown in FIG. 26. In thealternating-current impedance waveform, the transverse axis indicatesthe real part Z′ of the impedance, the ordinate axis indicates theimaginary part Z″ of the impedance, and the measurement frequencies of 1kHz and 1 Hz are marked with black dots.

(Consideration)

In Example 3, as is clear from FIG. 26, the internal resistance waslowered. The reduction in the reaction resistance (the interface chargetransfer resistance) accounts for the majority of the reduction in theinternal resistance, and thus the reduction may be achieved due todensification and increase of the connection interface area between theelectrode active material and the solid electrolyte material.

It should be understood that the all-solid-state cell of the presentinvention is not limited to the above embodiment, and various changesand modifications may be made therein without departing from the scopeof the invention.

1. An all-solid-state cell comprising positive and negative electrodeportions containing an electrode active material, an electrolyte portioncontaining a solid electrolyte, and positive and negative collectorportions, wherein one or both of the positive and negative electrodeportions are formed by mixing and firing the electrode active materialand an amorphous solid electrolyte material, and the electrode activematerial and the solid electrolyte material satisfy an inequality:Ty>Tz wherein Ty is a temperature at which a capacity of the electrodeactive material is lowered by a reaction between the electrode activematerial and the solid electrolyte material, and Tz is a temperature atwhich the solid electrolyte material is shrunk by firing.
 2. Anall-solid-state cell according to claim 1, wherein Tz is a temperatureat which the relative density of the solid electrolyte material isincreased to 70% or more of the theoretical density thereof due to theshrinkage by firing.
 3. An all-solid-state cell according to claim 1,wherein the solid electrolyte material comprises an amorphous polyanioncompound, and the one or both of the positive and negative electrodeportions are formed by mixing and firing the electrode active materialand the solid electrolyte material.
 4. An all-solid-state cell accordingto claim 1, wherein the solid electrolyte material comprises anamorphous phosphate compound, and the one or both of the positive andnegative electrode portions are formed by mixing and firing theelectrode active material and the solid electrolyte material.
 5. Anall-solid-state cell according to claim 4, wherein the solid electrolytematerial comprising the phosphate compound is of Nasicon type after thefiring.
 6. An all-solid-state cell according to claim 5, wherein thephosphate compound of the solid electrolyte material is LAGPLi_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ (0≦x≦1).
 7. An all-solid-state cellaccording to claim 5, wherein the phosphate compound of the solidelectrolyte material is LATP Li_(1+x)Al_(x)Ti_(2−x)(PO₄)₃ (0≦x≦1).
 8. Anall-solid-state cell according to claim 1, wherein the electrode activematerial is a Nasicon type material comprising a phosphate compound. 9.An all-solid-state cell according to claim 8, wherein the phosphatecompound of the electrode active material is LVP Li_(m)V₂(PO₄)₃ (1≦m≦5).10. An all-solid-state cell according to claim 1, wherein the electrodeactive material for the positive electrode portion is an olivine typepositive electrode active material comprising a phosphate compound. 11.An all-solid-state cell according to claim 10, wherein the phosphatecompound of the positive electrode active material is LNP Li_(n)NiPO₄,LCP Li_(n)CoPO₄, LMP Li_(n)MnPO₄ or LFP Li_(n)FePO₄ (0≦n≦1).
 12. Anall-solid-state cell according to claim 2, wherein the solid electrolytematerial and the electrode active material are of Nasicon type after thefiring.
 13. An all-solid-state cell according to claim 2, wherein thesolid electrolyte material and the electrode active material are ofNasicon type, the solid electrolyte material comprises LAGPLi_(1+x)Al_(x)Ge_(2−x)(PO₄)₃ (0≦x≦1), and the electrode active materialcomprises LVP Li_(m)V₂(PO₄)₃ (1≦m≦5) in both the positive and negativeelectrode portions, whereby the all-solid-state cell has a symmetricalstructure.
 14. An all-solid-state cell according to claim 1, wherein oneor both of the positive and negative electrode portions are formed byfiring under an applied pressure.
 15. An all-solid-state cell accordingto claim 1, wherein one or both of the positive and negative electrodeportions are formed from a paste for printing by firing it under aninert atmosphere.